A technique using a spin torque oscillator in a reproducing head of a magnetic recording and reproducing apparatus such as a hard disk drive (HDD) has been proposed. The spin torque oscillator reproducing head using the spin torque oscillator is considered to be able to avoid the problem of magnoise which is beginning to be a problem in the conventional HDD reproducing heads. In the spin torque oscillator reproducing head, magnoise is suppressed more as the oscillation of the spin torque oscillator becomes stabler, and a reproduction signal having a higher SN ratio (signal-to-noise ratio) can be obtained. As an issue on the spin torque oscillator reproducing head from a practical point of view, it is considered to be required to increase further the SN ratio of a reproduction signal by suppressing the medium noise such as the inter-track interference and inter-bit interference.
The processed shapes of the spin torque oscillator are roughly classified into two types: a pillar type and nanocontact type. The pillar type spin torque oscillator has a shape obtained by processing a multilayered magnetic film formed by an oscillation layer, spacer layer, and polarizer layer into a submicron-order pillar shape. On the other hand, the nanocontact type spin torque oscillator has a shape obtained by processing a contact electrode for supplying an electric current into a size on the submicron order without processing a multilayered magnetic film into any specific shape. The nanocontact type spin torque oscillator is considered to be able to obtain oscillation stabler than that of the pillar type spin torque oscillator. For example, it has been reported that oscillation having a high Q value of 18,000 can be achieved in a nanocontact type spin torque oscillator under an appropriate magnetic field environment. In the nanocontact type spin torque oscillator, the oscillation layer is not processed, so there is little processing damage at the side surfaces of the oscillation layer. This is considered the main reason why stable oscillations are obtained in nanocontact type spin-torque oscillators. From the fact, it is considered that decreasing processing damage in the oscillation layer results in stable oscillations.
For the implementation of the spin torque oscillator reproducing head, the stable oscillation of the spin torque oscillation and the suppression of the medium noise are required.